According to the Sydney Food Futures project, farmers around Sydney produced around 20 per cent of the city's agricultural food needs in 2011, a share that will drop to 6 per cent by 2031.

To be sure, the city is not heading for starvation. But there are a host of reasons to preserve working farm land within the Sydney basin, say academics, planners and farmers.

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Fruit grower Ed Biel in his orchard on his farm Wanaka at Oakdale.Credit:Kate Geraghty

"Do we really simply think that Sydney should be one suburb stretching from Goulburn to Port Macquarie?" said Tony Biffin, a dairy farmer near the near the village of Cawdor outside Camden.

"We seem to accept that there can be parklands and national parks and all the rest of it, but not that there should be farms within that mix as well," said Mr Biffin, whose family has been working in the area since arriving as tenant farmers for the Macarthurs more than 170 years ago.

In one sense, the pressure on farmers within Sydney – in areas of the Hawkesbury, and Wollondilly, and west of Penrith and Liverpool – are the same as those on the rest of the city: land prices are high.

But there are added complications for those attempting to work properties on the city's fringe. Neighbours on new estates might not like the smell or the sounds of farming practices, said Dana Cordell, a research principal at the Institute for Sustainable Futures.

Tony Biffin on the family-run Biffin Dairy in Cawdor near Camden.Credit:Kate Geraghty

"Farmers need viable commercial conditions, land security and a social licence to operate in the basin," she said.

The opposite problem can also apply. Farmers can become isolated when neighbouring plots of land are bought by land-bankers with no intention of, or incentive to, work the land.

"We're finding that with the invasion almost of land speculators that that's pushing the values of land up to extreme highs and we then pay more," said Mr Biffin, who pays $10,000 a year in rates, far more than farms of equivalent size west of the mountains.

About 20 minutes drive west of Mr Biffin's property, near the village of Oakdale, Ed Biel has been growing stone fruit for 30 years.

"Why should you have farming in the Sydney basin?" asked Mr Biel, who has spent long hours pondering the question.

He provides an environmental answer.

"From a point of view of pure air quality you wouldn't want to fill up that basin with people, or with industry or with houses," said Mr Biel, who now makes about 40 per cent of his income selling to weekend farmers markets.

"If you are looking at the liveability of the city, would you want to live in a city that is completely full of concrete and tiles and tar, or would you rather have somewhere that you could see that had some green space," he said.

Mr Biel, however, said the current political and planning answers tend to focus on zoning, which did not fix the problem.

Even when land was zoned for agriculture, there was little economic incentive to work land near Sydney. He is pushing a solution similar to that used to preserve the economic value of heritage buildings in inner Sydney: farmers who worked land could trade credits to developers to be used for more intensive development elsewhere.

For instance, the share of Sydney's vegetables locally produced would drop from 10 per cent to 1 per cent on current trends.

The share of fruit grown locally would drop from 2 per cent to 0 per cent. Local eggs would drop from 39 per cent to 2 per cent. Dairy would drop from 38 per cent to 18 per cent.

All of these trends, however, could be resisted. The project, which has been funded by Local Government NSW and the Office of Environment and Heritage and supported by Wollondilly Shire Council, also shows more optimistic outcomes if agriculture was prioritised in areas of outer Sydney.

"At the moment the planning system is very much focused on housing and infrastructure, and perhaps sees itself as a system that is designed to facilitate the increased supply of housing," said Laura Wynne, a Senior Research Consultant, Institute for Sustainable Futures.

"That is one of its purposes, but it also there to ensure land is used in a variety of ways that will be beneficial to the city," said Ms Wynne.

The state government has been continuing policies of releasing land to the north west and south west of greater Sydney.

Late last year, for instance, Planning Minister Rob Stokes released enough land for the construction of 35,000 homes south of Campbelltown.

A spokesman for the NSW Department of Planning said the government's Plan for Growing Sydney "recognises the importance of agriculture values and outlines the work to prepare a strategic framework for the metropolitan rural area".

The spokesman also said the new Greater Sydney Commission would prepare District Plans to held develop agricultural resources in the metropolitan rural area.

For Mr Biffin, however, there seems little immediate relief for the curious isolation of the metropolitan farmer.

"When we've been here for as long as we have and are planning to be here for a bit longer, it's kind of hard to cope or know what you are going to do," he said. "It sort of leaves you in a limbo."